Viscosity is a measure of a liquid's resistance to flow. The viscosity of a liquid is typically measured using instruments known as viscometers, e.g., tube-type (capillary), falling body (timed fall), and rotational (drag torque) viscometers. See, e.g., Rosencranz, R. and Bogen, S. A. Am. J. Clin. Pathol. 2006, 125(Suppl 1): S78-S86.